Genomics and proteomics research has elucidated many new biomarkers that have the potential to greatly improve disease diagnosis [2-3]. The development of rapid and inexpensive diagnostic assays adapted for point-of-care (PoC) applications would aid in the control of diseases [1]. The availability of multiple biomarkers is believed to be critical in the diagnosis of complex diseases like cancer [4], for which disease heterogeneity make tests of single marker inadequate. Hence, real-time detection of multiple biomarkers associated with different stages of disease pathogenesis could facilitate early detection of diseases [5]. However, widespread use of such biomarkers in disease diagnosis ultimately depends upon the development of field deployable biosensor devices. For PoC applications, biosensors are expected to allow real-time, rapid, label-free and multiplexed detection of biomarkers with high selectivity and sensitivity. Such devices would not only reduce time between sampling and responses but will also reduce costs by making tests available in environments where laboratory testing is unavailable or impractical [6].
Prevailing bio-detection systems mainly rely on fluorescence methods (label-based detection) to detect the binding of biomarkers to a biorecognition element. This includes the commonly used clinical approach for protein marker detection, enzyme-linked immunoabsorbent assay (ELISA). Though past research has demonstrated detection limits as low as few femtamolar concentrations (pg/ml) using fluorescence based detection, the need for sophisticated and costly instruments, long detection time and complicated process steps make label-based detection methods incompatible for hand-held portable biosensing applications [7]. Rapid, multiplexed, detection has not been attained with any existing label free detection schemes including surface plasmon resonance (SPR) [8-10], microcantilevers [11-14], carbon nanotubes [15-16] and quartz crystal microbalance [17]. Fan et al [18] reported an integrated microfluidic system which they called the integrated blood barcode chip (IBBC) to address the issue of multiplexed detection of protein in microliter quantities of blood. Though the chip proved to be a new approach for multiplexed immunoassays, it ultimately depends on fluorescent labels to detect the proteins of interest which makes it not suitable for portable and remote health monitoring application. A similar approach was used by Zheng et al [19] where nanowire sensor arrays were used for multiplexed electrical detection of cancer biomarkers.
Micro Electro-Mechanical Systems (MEMS) technology holds the potential to allow integrated sensors for the detection of biomarkers in hand held devices. Miniaturized sensor size aids in reducing measurement time and minimizing invasiveness. Recently, MEMS and related technologies have found interest in rapid label-free detection of biomarkers. Kim et al [20] demonstrated a detection method based on RF electric signals and MEMS to detect Glucose oxidase (GOx). Dalmay et al [21] developed a detection method using microwave frequencies to study cell electrical parameters.